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Impedance analyzer

A graphical impedance analyzer with good phase resolution is a must. Some brands have all the bells and whistles, but not the phase resolution necessary to accurately measure high Q (100+) components over the instrument's full frequency range (which should extend at least into the low megahertz). Of course the Agilent 4294A fills the performance bill, but with a $40k+ purchase bill, it also empties the budget (like similar high end new models from Wayne Kerr). Used models from Wayne Kerr work very well, and can be had for under $10K but they are very heavy and clunky with very ugly (but still useable) displays.

Perhaps the best value may be the Hioki IM3570, which works extremely well with superior phase resolution, has a very nice color touch screen display (with all the expected engineering graphing formats), is compact and lightweight, and costs around $10k new. Its only downside is that its fan is annoyingly loud and does not reduce its noise output during instrument idle.

But where should an impedance analyzer rank on the power electronics design engineer's basic equipment list (and why)?

Beyond the basic lower cost necessities such as DMMs, bench power supplies, test leads, soldering stations, etcetera, I would rank a good impedance analyzer second only to a good oscilloscope. The impedance analyzer allows one to see all of a component's secondary impedance characteristics and to directly compare similar components. Often overlooked is the information such an instrument can provide by examining component assemblies in situ in a circuit board assembly. Sometimes this can be very revealing of hidden, but influential layout parasitics.

Equally importantly, an impedance analyzer allows accurate SPICE models to be quickly formulated so that simulation can be used as a meaningful design tool. Transformer magnetizing and leakage inductances can be measured as well as inter-winding capacitance and frequency dependent resistive losses. From these measurements and with proper technique, a model can be formulated that nearly exactly matches the real part. Not only does this allow power circuits and control loops to be initially designed entirely by simulation (under the judicious eye of experience, of course), but it even allows one to effectively simulate the low frequency end of a design's EMI performance.

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